CommentPress is an open source theme and plugin for the WordPress blogging engine that allows readers to comment paragraph-by-paragraph, line-by-line or block-by-block in the margins of a text. Annotate, gloss, workshop, debate: with CommentPress you can do all of these things on a finer-grained level, turning a document into a conversation. It can be applied to a fixed document (paper/essay/book etc.) or to a running blog. Use it in combination with multisite, BuddyPress and BuddyPress Groupblog to create communities around your documents. http://www.futureofthebook.org/commentpress/
http://www.futureofthebook.org/commentpress/